User:Sanuja Mohanaraj/Notebook/Experimental Biochemistry 1 Fall 2017/2017/09/12

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Buffer Solutions Preparation

To begin preparing the 0.1M Na2HPO4/Na3PO4 buffer solution at a pH value of 10, 3.549grams of Na2HPO4 and 0.01962grams of Na3PO4 were weighed out into a 0.25L volumetric flask. Deionized water was then added to the flask, to the mark. This was then repeated twice to yield two buffer solutions of pH values 11 and 12.

Next, nine solutions of Au:AA were prepared using the three amino acids (phenylalanine, arginine and isoleucine) and the buffer solutions at the three different pH values.

10mM HAuCl4 & 100mM Arginine Stock Solutions Preparation

A 10mM HAuCl4 solution was then prepared by diluting ~0.8495grams of HAuCl4 with deionized water in a 0.25L volumetric flask. Similarly, a 100mM arginine solution was also prepared by diluting ~0.6968grams of arginine with deionized water into a 0.04L volumetric flask. Next, eighteen separate gold nanoparticle solutions were prepared using the 100mM arginine solution and the three different buffer solutions, at varying molar ratios (10:1, 1:1 and 1:10), before setting aside for overnight heating.


Figure 5 illustrates the formation of AuNPs from amino acid-stabilized gold colloids in buffer solutions instead, of the three amino acids – arginine (Figure 5a), phenylalanine (Figure 5b) and isoleucine (Figure 5c) – at pH values of 10, 11 and 12. The arginine-stabilized gold solution (Figure 5a), at pH 12 is the only solution that formed AuNPs, which suggests that Arginine was the optimal amino acid in reducing Au3+ to Au0.


          Figure 5a


          Figure 5b


          Figure 5c

Figure 6 depicts the AuNPs formed using arginine-stabilized gold solutions at Au:Arg molar ratios of 10:1, 1:10 and 1:1; and at pH values of 10, 11 and 12. Again, arginine was chosen as the optimum amino acid in causing the reduction of gold, due to nitrogen's lone electron pair on the arginine's side chain. According to Figure 6, colloidal gold solutions were formed at Au:Arg molar ratios of 10:1 and 1:10. However, the color change of the gold nanoparticle solution to blue could indicate that the solution is in the aggregated state.


          Figure 6a


          Figure 6b


          Figure 6c


0.1M Buffer Solutions st pH values 10, 11 and 12
pH = pKa+ log([base]/[acid])
pKa = 12.32 [H] = 0.1M

pH 10 Calculations
pH = pKa + log([base]/[acid])
10 = 12.32 + log([base]/[0.1])
[base] = 4.7863e-04 M

moles / 0.25L = 4.7863e-04 M
moles = 1.1965e-04

grams / (163.94g/mol) = 1.1965e-04 moles
grams of Na3PO4 = 0.019616 grams

moles / 0.25L = 0.1 M
moles = 0.025
grams / (141.96 g/mol) = 0.025 moles
grams of Na2HPO4 = 3.549 grams

These calculations were also done for pH values 11 and 12 as well.

10mM HAuCl4 Stock Solution
Molarity = moles / volume
10mM = moles / 0.25L
Moles = 0.0025 moles

Moles = grams / molar mass
0.0025 moles = grams / (339.785 g/mol)
grams = 0.8495 grams of HAuCl4